Ultra-high capacity and ultra-long cyclability anode materials of non-layered vanadium carbide(V8C7)@carbon microspheres for biapplications in Li-ion battery and Li-ion capacitor

Abstract

The main factor affecting the electrochemical performance of Li-ion hybrid capacitor (LIHCs) is the imbalance of kinetics between anode and cathode. Although 2D Layered Mxenes widely applied to energy storage owing to their remarkable electrical conductivity and adjustable interlamellar spacing, the synthesis process is time-consuming and hazardous. Therefore, Non-layered transition metal carbides (TMC) have gradually become a research hotspot. Herein, a facile two-step method is reported to synthesize the V8C7 nanoparticles grown in situ in carbon microspheres (V8C7 @CMs). The V8C7 @CMs provide high specific capacity (774 mAh g−1 after 330 cycles at 0.1 A g−1) in half cell. The long cycle stability with extraordinary rate capability (150 mAh g−1 after 5000 cycles at 1 A g−1, 100 mAh g−1 - 13000 cycles - 2 A g−1, and 70 mAh g−1 - 20000 cycles-5 A g−1) can be demonstrated. In order to realize the construction of high-performance LIHCs, it is also very important to design the cathode materials reasonably. So, the cathode material, nitrogen doped grapefruit peel biochar (NGPB), with outstanding rate performance and superior cycle stability, was designed and synthesized by the method of calcination. The performance tests indicates that the specific capacity is kept at 125 mAh g−1 after 2000 cycles at 1 A g−1, 120 mAh g−1-2000 cycles-2 A g−1 and 115 mAh g−1-2000 cycles-5 A g−1. Then, the constructed V8C7 @CMs//NGPB-2 LIHCs demonstrates high power density (PD) (9358 W kg−1), energy density (ED) (95.55 Wh kg−1) and excellent long cycle stability (a capacity retention rate of 74.7% after 10,000 cycles at 0.1 A g−1, 77%−5000 cycles-1 A g−1). Based on the above research, it is found that the key to realize high-performance LIHCs is to develop long-cycle stable and super rate capability anode materials.